The present invention relates to an improved method for stabilizing a thin film of a composite lubricant material applied to the surface of a thin film recording medium, particularly for reducing static and dynamic frictional coefficients thereof when utilized in combination with a flying head read/write transducer, and to improved thin film recording media obtained thereby. The invention finds particular utility in the manufacture and use of thin film type magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of thin film layers formed on a suitable substrate, e.g., a disk-shaped substrate, wherein a thin topcoat layer comprised of a composite lubricant material is applied to the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducer heads operating at very low flying heights.
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Alxe2x80x94Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Nixe2x80x94P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Crxe2x80x94V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (xe2x80x9cDLCxe2x80x9d) having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate typically comprises a reflective layer, e.g., of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disk form, such as described supra, are typically lubricated with a thin topcoat film or layer comprised of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out transducer heads operating at low flying heights, as in a hard disk system functioning in a contact start-stop (xe2x80x9cCSSxe2x80x9d) mode. Conventionally, the thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether.
The lubricity properties of disk-shaped recording media are generally measured and characterized in terms of dynamic and/or static coefficients of friction. The former type, i.e., dynamic friction coefficient, is typically measured utilizing a standard drag test in which the drag produced by contact of a read/write transducer head with a disk surface is determined at a constant spin rate, e.g., 1 rpm. The latter type, i.e., static coefficients of friction (also known as xe2x80x9cstictionxe2x80x9d values), are typically measured utilizing a standard contact start/stop (xe2x80x9cCSSxe2x80x9d) test in which the peak level of friction is measured as the disk starts rotating from zero (0) rpm to a selected revolution rate, e.g., 5,000 rpm. After the peak friction has been measured, the disk is brought to rest, and the start/stop process is repeated for a selected number of start/stop cycles. An important property of a disk which is required for good long-term disk and drive performance is that the disk retain a relatively low coefficient of friction after many start/stop cycles or contacts with the read/write transducer head, e.g., 20,000 start/stop cycles.
The most commonly employed lubricants utilized with thin film, disk-shaped magnetic and MO media, i.e., perfluoropolyether (xe2x80x9cPFPExe2x80x9d)-based lubricants, perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Studies, as described in, for example U.S. Pat. No. 5,587,217, the entire disclosure of which is incorporated herein by reference, have indicated that the tribological properties, and perhaps corrosion resistance, of perfluoropolyether-based lubricants utilized in the manufacture of thin film recording media can be substantially improved by addition thereto of an appropriate amount of a cyclotriphosphazene-based lubricant additive, e.g., a polyphenoxy cyclotriphosphazene comprising substituted or unsubstituted phenoxy groups, to form what is termed a xe2x80x9ccomposite lubricantxe2x80x9d.
Currently, bis (4-fluorophenoxy)xe2x80x94tetrakis (3-trifluoromethyl phenoxy) cyclotriphospazene (available as X-1P(trademark) from Dow Chemical Co., Midland, Mich.) is the lubricant most commonly with perfluoropolyether-based lubricants for forming composite lubricants for use with thin film magnetic and MO media. However, as disclosed in U.S. Pat. Nos. 5,718,942 and 5,908,817, the disclosures of which are incorporated herein by reference, the use of X-1P as a lubricant additive for forming composite lubricants comprising commonly employed perfluoropolyether-based lubricants in the data storage industry (e.g., Fomblin Z-DOL(trademark) and Fomblin Z-TETRAOL(trademark), each available from Ausimont, Thorofare, N.J.) incurs a disadvantage in that the former (i.e., the cyclotriphasphazene-based lubricant additive) has very low solubility in the latter (i.e., the PFPE-based primary lubricant).
For example, X-1P, in combination with Z-DOL at levels up to about 5 wt. %, reduces stiction and increases the stability of Z-DOL. However, because X-1P is virtually immiscible in PFPE-based lubricants, phase separation typically occurs at the optimal X-1P/PFPE ratios. The phase separation leads to chemical non-uniformity of the lubricant film on the media (e.g., disk) surface, as by the so-called xe2x80x9cballingxe2x80x9d effect, which tends to affect the tribology (i.e., durability) of the head/disk interface, particularly when the thickness of the X-1P exceeds about 1-2 xc3x85. As a consequence of the poor compatibility of the X1P lubricant additive with the Z-DOL or Z-TETRAOL primary lubricant, the maximum amount of X1P that can used therewith is severely limited, typically to about 10% of the total lubricant thickness. Moreover, X-1P/PFPE mixtures do not exhibit performance enhancement over PFPE alone when the X-1P layer thickness is less than about 1xc3x85, or at X-1P concentrations less than about 1 wt. %. Thus, according to current practice, the effective concentration window for use of X-1P in combination with PFPE is quite narrow, and special process control is required to achieve optimal performance. Notwithstanding such special process control, phase separation of the X-1P additive, accelerated lubricant loss, and a large amount of transducer head smear frequently occur even with such low additive contents.
U.S. Pat. No. 6,099,762, the entire disclosure of which is incorporated herein by reference, discloses a process for enhancing the bonding, thus durability, of thin lubricant layers comprised of a PFPE, a phosphazene, or both, to media surfaces by means of a process comprising exposing the lubricant layer or film to infra-red (xe2x80x9cIRxe2x80x9d) and ultra-violet (xe2x80x9cUVxe2x80x9d) radiation, either simultaneously or sequentially, wherein the IR radiation effects heating of the lubricant layer or film to a temperature above about 150xc2x0 F. but less than about 500xc2x0 F., and the UV radiation comprises a wavelength component of about 185 nm for photolytically generating ozone (O3) in the vicinity of the lubricant layer or film for effecting bonding thereof to the media surface. This process for enhancing bonding of the composite lubricant films to the media surface, however, is not performed in a manner as to effect stabilization of the composite lubricant films.
In view of the above, there exists a clear need for improved methodology for applying thin films of composite lubricants to surfaces of thin film recording media, e.g., in disk form, wherein the composite lubricant films include a primary lubricant material comprised of a perfluoropolyether compound and a lubricant additive comprised of a cyclotriphosphazene derivative, which methodology overcomes the drawbacks and disadvantages of the conventional methodology described above. More specifically, there exists a need for improved methodology for applying and treating (e.g., for stabilizing with respect to phase separation) composite lubricant films comprised of a primary lubricant and a lubricant additive when utilized with disk-shaped workpieces in the manufacture of thin film magnetic and MO media.
The present invention addresses and solves problems and difficulties in achieving stabilization of high performance, composite lubricant thin films utilized in the manufacture of thin film, disk-shaped magnetic and MO data/information storage and retrieval media, wherein the composite lubricant thin films are comprised of a primary lubricant and a lubricant additive, while maintaining full compatibility with all aspects of conventional automated manufacturing technology therefor, including productivity requirements necessary for economic competitiveness. In addition, the present invention provides improved thin film magnetic and MO media having stabilized lubricant films comprised of a primary lubricant and a lubricant additive. Further, the methodology afforded by the present invention enjoys diverse utility in the manufacture of various other devices and/or article requiring formation of stable, high performance, composite lubricant thin films thereon.
An advantage of the present invention is an improved method for performing in situ stabilization of a composite lubricant to reduce or substantially eliminate phase separation of the components of the composite lubricant.
Another advantage of the present invention is an improved method for forming data/information storage and retrieval media comprising an in situ stabilized thin film or layer of a composite lubricant.
Still another advantage of the present invention is improved data/information storage and retrieval media comprising an in situ stabilized thin film or layer of a composite lubricant.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a method of performing in situ stabilization of a composite lubricant in order to reduce or substantially eliminate phase separation of the components of the composite lubricant, which method comprises the sequential steps of:
(a) providing a substrate including a surface;
(b) applying a thin layer or film of the composite lubricant to the substrate surface, the composite lubricant comprising at least two lubricant components which are normally mutually immiscible, leading to separation into individual phases over a period of time; and
(c) treating the thin layer or film of composite lubricant solely with UV radiation for an interval sufficient to reduce or substantially eliminate the phase separation of the at least two normally mutually immiscible lubricant components.
According to embodiments of the present invention, step (a) comprises providing a data/information storage and retrieval medium as the substrate, e.g., in the form of a disk-shaped magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) medium, wherein the substrate surface comprises a layer of a carbon (C)-based material; and step (b) comprises applying a thin layer or film of a composite lubricant comprising at least one perfluoropolyether compound as a primary lubricant and at least one phosphazene derivative as a lubricant additive, e.g., bis (4-fluorophenoxy)xe2x80x94tetrakis (3-trifluoromethyl phenoxy) cyclotriphosphazene.
In accordance with alternative embodiments of the present invention, step (b) comprises applying the thin layer or film of a composite lubricant in the form of a single layer containing the at least one perfluoropolyether compound and the at least one phosphazene derivative, or step (b) comprises applying the thin layer or film of a composite lubricant in the form of separate sub-layers of the at least one perfluoropolyether compound and the at least one phosphazene derivative.
According to embodiments of the present invention, step (c) comprises treating the thin layer or film of composite lubricant solely with UV radiation from a source which principally supplies UV at energies below the threshold energy for photolytic generation of ozone (O3); e.g., step (c) comprises supplying the UV radiation in the wavelength range from about 185 to about 254 nm, with about 70-80% of the radiation being at about 254 nm.
In accordance with further embodiments of the present invention, step (c) further comprises preventing contact of the thin layer or film of composite lubricant with oxygen (O2) during the UV irradiation, whereby the photolytic generation of O3 is further minimized or substantially prevented.
According to a particular embodiment of the present invention, the method forms part of a process for the manufacture of a data/information storage and retrieval medium, wherein:
step (a) comprises providing as the substrate a disk-shaped magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) medium, wherein the substrate surface comprises a layer of a carbon (C)-based material;
step (b) comprises applying a thin layer or film of the composite lubricant to the substrate surface, the composite lubricant comprising at least one perfluoropolyether compound as a primary lubricant and at least one phosphazene derivative as a lubricant additive; and
step (c) comprises treating the thin layer of composite lubricant solely with UV radiation from a source which principally supplies UV at energies below the threshold energy for photolytic generation of ozone (O3), and further comprises preventing contact of the thin layer or film of composite lubricant with oxygen (O2) during the UV irradiation, whereby the photolytic generation of O3 is further minimized or substantially prevented.
Another aspect of the present invention is a data/information storage and retrieval medium, comprising:
(a) a substrate including a surface; and
(b) a thin layer or film of an in situ stabilized composite lubricant on the substrate surface, comprising at least two normally mutually immiscible lubricant components treated solely with UV radiation to reduce or substantially eliminate phase separation thereof.
According to embodiments of the present invention, the substrate (a) is disk-shaped, comprises a layer stack including at least one magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) recording layer, and the substrate surface comprises a layer of a carbon (C)-based material; and
the thin layer or film (b) of stabilized composite lubricant on the substrate surface comprises at least one perfluoropolyether compound as a primary lubricant and at least one phosphazene derivative as a lubricant additive.
According to a particular embodiment of the present invention, the at least one phosphazene derivative comprises bis (4-fluorophenoxy)xe2x80x94tetrakis (3-trifluoromethyl phenoxy) cyclotriphosphazene.
In accordance with alternative embodiments of the present invention, the thin layer or film (b) of stabilized composite lubricant on the substrate surface is in the form of a single layer containing the at least one perfluoropolyether compound and the at least one phosphazene derivative; or the thin layer or film (b) of stabilized composite lubricant on the substrate surface is in the form of separate sub-layers of the at least one perfluoropolyether compound and the at least one phosphazene derivative.
According to a particular embodiment of the present invention, the sub-layer of the at least one perfluoropolyether compound is about 10-15 xc3x85 thick and the sub-layer of the at least one phosphazene derivative is up to about 5 xc3x85 thick.
Still another aspect of the present invention is a data/information storage and retrieval medium, comprising:
a substrate including a surface; and
means for providing a stabilized composite lubricant layer on the substrate surface.
In accordance with an embodiment of the present invention, the substrate comprises a layer stack including at least one magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) recording layer.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.